[Jeff Walker]

Just thought I would share this link about info on crankshaft thrust bearing failures. A bit of a long read, but IMO, some really good info. http://www.atra.com/crankshaft/

[R J Staub]

Thanks for the article. Very good read! Excellent info for those of us just starting out building their own motors... I;m filing it away for future use. & I think the mod that they talk about for the thrust bearings is similiar to the one that P-Dude recommends, although it is hard to see in their pics...
http://www.angelfire.com/fl4/pontiac...earingmod.html

[Half-Inch Stud]

I concur

[Will]

As one who has suffered repeat thrust bearing failures without an obvious cause, that was very interesting reading. Thanks much!

[Malky]

I am in the middle of a mysterious thrust brg failure myself on a SBC, 50 miles after a rebuild. I found this article and a few others like it googling. I will do the brg mod and check for high TC pressure on the tranny cooler inlet line.

[Jeff Walker]

If you do find high TC pressure you better take the pan of the trans and see if there is an abnormal amount of material in the pan. The article that I posted stated that if thrust bearing failure is transmission related it will usually damage the transmission too.

[GRX]

Great article!
My favorite part is where they mention surface finish. I have been in heated discussions about that more than once. Many believe the thrust should have the cross-hatch to move the oil much the same as on the cylinder walls. However I always polished the thrust smooth when I ground a crank. Never had an issue. Then again I was not building racing engines either. More for longevity than performance in most cases.

[RAIV55]

I had a couple issues concerning that article. First the asumption that something is jammed when the statement was made about transmission damage. True if the pump/converter doesn't have enough endplay either by reversing the inner pump gear or freeplay between the converter to flexplate... it will eat the pump. The second thing is minor, but the area calculation was in error, should be going off the OD of the converter hub.

Rest of the article was pretty much in line with what was posted on an AERA bulletin I read.

[Pontirag]

I've always gave the crank a bit of a smack forward with a dead blow hammer to seat both halves of the thrust bearing as far forward as is reasonable, specificly to seat both of them and to ensure that they both rest firmly against the face of the thrust surface and both of those bearing halves are seated firmly against thier respective surfaces on the main cap and engine bearing "saddle". if not two possible outcomes:
1. If one bearing half is seated and the other is not then at some point early in the start up of a fresh rebuild the crank will force the improperly seated thrust bearing half forward. not good for a properly torqued maincap as the bearing must be able to slide forward. something it cant possibly do when the main cap is properly torqued but something it will do catostrophically.
2. ditto if both bearing halves are not seated properly as far forward as is possible. the crank as it breakes in upon start up will force both halves forward under about the most imposible curcumstances possible and the bearing itself and its fragile surface is the weak link and it will fail.

Another precaution should also be noted. If you put a high pressure/ heavy duty pressure plate on a car that has some miles on it that increased pressure will transmit that pressure forward to the thrust surface of that bearing and even a low milage engine will sustain increased wear. a high milage engine will most likely fail in short order, especially if you have numericaly high number rear gears or bigger tires.

I've also noticed an increased likelyhood that the rear main seal will also fail (begin to leak) if you've converted a medium to high milage auto trans engine to a manual trans. The forward movement experienced as the clutch is operated moves the crank back and forth starts to work over a broken in and perhaps tired seal.

[Geoff]

Great article. I didn't see any mention of the flex plate function.

I have always wondered about the 'stiffness' or 'spring' in the flex plate & what it's roll is, if any, in absorbing some of the force the converter trying to push forward. If the flexplate was 1/4" thick, it is very rigid, no longer really a 'flex' plate, more a rigid plate; any force the converter generates will be transmitted forwards in it's entirety by a 1/4" plate. A thinner 1/8" flex plate I would think will bend with the quoted 210 lbs of force applied to it, acting like a spring being compressed, absorbing some of the force.
Are some of the extra thick performance flex plates contributing to the thrust failures?

[P@blo]

OK, what the heck do they put in the water down there and can you send me some.

Geoff, your posts are always full of great information and were lucky to have you posting on the PY forum.